1. Field of the Invention
The present general inventive concept relates to print quality evaluation of a printer, and more particularly, to a method and apparatus to evaluate the print quality and to indicate the evaluation results.
2. Description of the Related Art
Printer resolution is one measure of print quality of a printer and refers to a level of detail that can be achieved when an image is printed on a medium. As a unit of resolution, dots per inch (DPI) generally refers to a density of printed dots, such as those used in halftone printing, that remain distinguishable from neighboring dots, although not necessarily with the naked eye.
In general, conventional operations of measuring the resolution of the printer are described as follows. In order to measure the resolution, pattern data are used that include bar patterns in which a highlight portion and a shadow portion having widths corresponding to each of a plurality of predetermined resolution values are repeated. For example, in a bar pattern corresponding to a resolution of 50 DPI, highlight and shadow bars having a width of 1/50 of an inch are repeated, and in a bar pattern corresponding to a resolution of 600 DPI, highlight and shadow bars having a width of 1/600 of an inch are repeated, as illustrated in FIG. 1. It is to be observed from FIG. 1 that the repetition of the bars at high resolution is not clear to the naked eye.
The pattern data are printed on a medium of the printer so as to be evaluated, and a reflectance is measured by scanning the printed medium using light. Thereafter, an average of reflectances with respect to a direction of a length of the bar pattern is obtained to produce a reflectance profile in a 1D direction. Here, a position of each bar pattern can be identified by its position relative to a position detection marker, as illustrated in FIG. 1. Next, a maximum value and a minimum value of the reflectance profile is calculated for each bar pattern corresponding to each resolution, and a contrast value C is calculated for each bar pattern corresponding to each resolution by using the following equation.
                    C        =                                            R              max                        -                          R              min                                                          R              max                        +                          R              min                                                          [                  Equation          ⁢                                          ⁢          1                ]            
Here, Rmax and Rmin denote the maximum value and the minimum value of the reflectance profile, respectively.
As described above, a contrast value is calculated for each resolution of the pattern illustrated in FIG. 1, the calculated values are plotted to be compared with a predetermined threshold in order to calculate a resolution limit that is a resolution value at which the calculated contrast value meets the predetermined threshold. Thereafter, the calculated resolution limit is used as an indicator of print quality.
In the conventional method of evaluating print quality, deterioration of print quality that occurs due to a mismatch of a print position caused by printer characteristics or a defect of the printer is not considered. This will be described with reference to FIG. 2.
The left side of FIG. 2 illustrates print results, and the right side thereof illustrates changes in the reflectance according to a print position. An ideal print result is illustrated in (a). In the aforementioned method of evaluating print quality, the contrast value is calculated by using only the maximum value and the minimum value of the reflectance profile in the 1D direction, so that (b) and (c), which represent mismatched print position, and (d), which represents that both a print width and a print position are not correctly printed, have the same contrast value as that of the ideal print result (a). As a result, the print quality of mismatched patterns is evaluated to be the same as an ideal print pattern.
FIG. 3 is a view to explain another problem of the conventional method of evaluating print quality. Similar to FIG. 2, the left hand portion illustrates a print result, and the right hand portion illustrates a change in reflectance according to a print position. In the conventional method of evaluating print quality, the contrast value is calculated using only the maximum value and the minimum value of the reflectance profile in the 1D direction, so that (b), which represents a change in print gradation, and (c), which represents mixing noise components to the ideal profile (a), have the same contrast value as that of the ideal profile (a). Therefore, although there is a change in print gradation and mixing with noise components, print quality may be inaccurately evaluated.